Preheat oven to 400F.,In a small bowl, combine oil, basil, oregano, salt, garlic powder, and pepper; mix well.,Place mushrooms, tomatoes and onions in a ungreased 13x9 inch baking dish.,Brush about half of the oil mixture on the vegetables.,Arrange chicken over vegetables.,Brush with remaining oil mixture.,Bake for 50 to 60 minutes, or until chicken is done.,Spoon pan juices over chicken halfway through baking.,______